As one skilled in this art appreciates, air foil bearings are extremely sophisticated and highly technical devices and alterations, changes and additions to the composition and configuration of these types of bearings are very critical and can materially affect the operation thereof. An example of a hydrodynamic fluid film thrust bearing is disclosed in U.S. Pat. No. 4,462,700 granted to G. L. Agrawal on Jul. 31, 1984 entitled "Hydrodynamic Fluid Film Thrust Bearing" and commonly assigned to United Technologies Corporation. This invention constitutes an improvement over the thrust bearing disclosed in this patent.
Typically, the thrust bearing includes a stationary thrust plate, a rotating thrust runner axially spaced therefrom, and one or two foils disposed therebetween. Each of the foils include backing members having different relative spring rates. In the thrust bearing that includes two foil corrugated backing members, the foil member adjacent to the rotating thrust runner typically is a corrugated metallic member with a relatively high spring rate which has a higher spring constant than the foil member adjacent the stationary thrust plate. This serves to establish and maintain an optimum fluid film geometry under all loading, speed and other operating conditions. The other backing member which has the lower relative spring constant provides the bearing with compliance for adequate load capacity and damping characteristics. It is to be understood that for certain applications it is beneficial to design both backing members to have equal spring rates to achieve particular performance parameters.
As is well known in this technology the surface of the washer shaped thrust bearing foil plate is fitted with a plurality of wedge shaped corrugated thrust bearing bump foils (segments) spaced about the circumference. The leading edge of the corrugated thrust bearing bump foils are welded to the face of the thrust bearing foil plate and the opposite end is unattached and free to move axially. The top foil which is similarly shaped to the corrugated thrust plate is likewise welded at the leading edge to the thrust bearing foil plate. The leading edge of the top foils is spaced just upstream of the leading edge of the corrugated thrust bearing bump foils. Depending on the particular application, the thrust bearing will consist of several of such segments and the number of segments utilized will principally depend on the optimized performance of such application.
To obtain damping the thrust bearing includes a second washer shaped backing spring foil plate and a plurality of corrugated backing spring bumper foils. Each of the corrugated backing spring bumper foils are identical in shape and size to each of the corrugated thrust bearing bump foils and their leading or trailing edges are welded to the face of the backing spring foil plate and the opposite end is unattached. The thrust bearing bump foil is attached to the upper face of the foil plate and the backing spring bump foil is attached to the lower face of its foil plate.
As is well known in this technology, the practice is to axially align the leading edges of the thrust bearing bump foil with the leading edges of the backing spring bump foil. Thus the leading edges and their respective weld joints of all the segments are in axial alignment with each other.
I have found that I can increase thrust bearing load capacity while at the same time reduce running torque by a significant amount by offsetting the leading edge of the thrust bearing bump foil relative to the leading edge of the backing spring bump foil. This improvement in the thrust bearing makes the difference in certain applications of meeting the thrust bearing requirements of certain rotating machinery.